The present invention relates to a manufacturing method of wiring board having a semiconductor LSI and a ceramic substrate, and a conductive paste used therein.
Recently, semiconductor LSI and solid composite parts are more and more reduced in size and weight, and the wiring boards for mounting them are also required to be smaller and lighter. To meet such demands, the ceramic substrate is capable of wiring at density as high as demanded, and hence the ceramic substrate is highly noticed today in the electronics industry.
As the wiring pattern forming method, Japanese Patent Publication No. 6-20035 discloses a method of applying a conductive ink by using an intaglio printing method. Japanese Laid-open Patent No. 9-246125 discloses a method of adhering an electrode material layer to a substrate by using a heat transfer film.
The patterns transferred by these prior arts have a thin film thickness. Accordingly, when such transferred patterns are used as fine patterns, the wiring resistance is heightened.
Japanese Patent Publication No. 3-20914 discloses a method of fabricating fine lines for realizing high density wiring. That is, it proposes a method comprising a step of filling the intaglio grooves of a flexible resin film with a conductive paste and drying, a step of transferring the conductive paste onto a substrate having an adhesive layer, and a step of baking the substrate and forming the conductive pattern. This method is capable of forming a fine conductive pattern, and moreover since the wiring resistance is lowered, the conductive pattern having a thick film thickness is formed. Hence, this method is an effective wiring forming method for fabricating high density wiring.
In this method, however, since the conductive paste is transferred on the adhesive layer on the substrate, and the adhesive layer and conductive paste are baked at the same time, the adhesive layer is softened and removed, and due to the effects at this time, the conductive pattern formed of the conductive paste placed on the adhesive layer may be deformed.
That is, before completion of combustion of the adhesive layer, if the resin component contained in the conductive paste is burnt completely or partly, conductive particles of the conductive paste may be burnt completely or partly without adhering to the substrate. Accordingly, sufficient adhesion strength of the conductive paste is not obtained, and the conductive pattern formed of the conductive paste is deformed. As a result, it was difficult to form a fine pattern of high precision.
The invention is devised to solve these problems, and to realize a fine pattern forming of high precision by using film intaglio transfer method, it is an object of the invention to present a manufacturing method of wiring board in consideration of materials such as adhesive layer and conductive paste so that the conductive particles of the conductive paste may be baked on the substrate without having effects of combustion of the adhesive layer, and also in consideration of peeling off the conductive pattern from the intaglio grooves, and a conductive paste used therein.
A manufacturing method of wiring board of the invention comprises:
(a) a step of forming an adhesive layer on the surface of a ceramic substrate,
(b) a step of forming grooves having a wiring pattern shape on a film,
(c) a step of filling the grooves with a conductive paste containing a conductive component and a resin,
(d) a step of adhering the conductive paste side surface of the film having the conductive paste to the adhesive layer side surface of the ceramic substrate having the adhesive layer,
(e) a step of forming a conductive pattern on the adhesive layer surface by peeling off the film from a first laminated body having the film, conductive paste, adhesive layer, ceramic substrate, and film, and transferring the conductive paste filling up the grooves onto the surface of the adhesive layer, and
(f) a step of firing a second laminated body having the ceramic substrate, adhesive layer and conductive pattern, removing the adhesive layer, and sintering the conductive particles,
in which the conductive component in the conductive paste is sintered at least one of (i) after the adhesive layer is softened, and (ii) after the adhesive layer is burnt.
Preferably, at the step (f), the resin contained in the conductive paste is burnt and removed after the adhesive layer is burnt and removed.
A conductive paste of the invention used in forming of a conductive pattern on a wiring board having an adhesive layer, a resin component as binder, and a solvent, in which the resin contains plural resins which are burnt and removed in a temperature having range from a temperature range of 150 to a temperature range of 360xc2x0 C. at the time of firing.
Preferably, the resin contains plural resins which are burnt and removed in a temperature range for burning the adhesive layer.
In this constitution, at the time of firing, since the conductive particles of the conductive paste are sintered after softening or burning of the adhesive layer, the conductive particles can be sintered regardless of softening or removal of the adhesive layer, so that a conductive pattern wiring of excellent shape having high density and high precision can be obtained.